C. Crescentus is a gram-negative microorganism that divides unequally to produce a non-motile stalked cell and a smaller, flagellated swarmer cell, each with different developmental sequences. This organism is an ideal model system for the study of stem cell differentiation. Two related aspects of development in C. crescentus are of interest. (1) Temporal patterns - How is the program for an ordered series of structural and functional changes encoded in a cell? and (2) Spatial patterns - How is structure and functional information localized within a cell in a way to lead to unequal cell division? Our main approaches to studying the molecular mechanisms that control the temporal aspects of this control are the following. A. A genetic analysis is being used to determine which cell cycle events are responsible for regulation of periodic protein synthesis in Caulobacter. Specifically, the induction and shut off of the flagellar proteins, flagellin and hook protein, are being examined in conditional cell cycle mutants and in mutants which are deregulated in some way for expression of one of these proteins. B. To examine how expression of flagellar or other developmental proteins are coupled to the cell cycle we plan to isolate the regulated genes by molecular cloning in order to study their structure and their expression in vitro. A preliminary stage in this analysis is isolation and characterization of the ribosomal genes from Caulobacter.